The invention relates generally to battery packs, and more particularly to battery packs which are easy to assemble and disassemble.
The battery assembly for hybrid or plug-in electric vehicles (EV) may consist of a plurality of battery cells 10, cooling fins 15, repeating frames 20, and foam sheets 25, which are stacked and joined together to form a module or pack as shown in FIG. 1. Although the battery cells are the only energy and power source of the battery, the assembly needs the other components to form a fully functional and reliable system. All of them add weight and complexity to the battery pack. For example, the total weight of the repeating frames can be as much as 10% of the total weight of the battery pack.
The battery for a long driving range EV may contain more than 200 battery cells. The cells are preferably in prismatic shape for better spatial energy density and thermal efficiency. The individual number of cooling fins, repeating frames, and foam sheets can be half as many as the number of battery cells. Each part possesses different material properties and a different geometric shape. The battery cells are semi-rigid and laminated in a pouch. The cooling fins, which can be made of a single piece of aluminum or two aluminum sheets welded together with coolant passages inside for example, are prismatic and thin, but stiffer than the battery cells. The foam sheets, which provide space for thermal expansion and compression, are relatively soft and have rubber gasket borders. The plastic repeating frames, which are narrow and hollow, have intricate interlocking details and coolant seals on both sides of the frame. The large number of different parts makes a fast stacking operation challenging enough. The differences in physical form and properties further increase the difficulty and complexity of automated assembly, requiring costly assembly equipment or causing a slower assembly operation.
Typically, after stacking and assembling the battery components into a module, every two or three adjacent battery cells are welded together to form parallel electric connections. Each cell has at least two tabs or electric terminals (one positive, one negative) for such welding. An interconnect board can be added and welded to the cells to complete the serial connection of the battery pack, if desired. The welding operations require proper welding machines and tooling, and they are expensive and time consuming operations. Furthermore, due to the difficulty of precise tab bending and height control, the protrusion of any tabs after welding poses the risk of an electric short with the battery monitor board attached on top of the battery pack.
Finally, due to the irreversible nature of current welding techniques, such as spot welding and ultrasonic welding, removing a bad cell from a fully assembled battery pack requires cutting all the tab connections in the module. Thus, the good battery cells are unable to be re-welded, which is an expensive product and manufacturing problem.
Therefore, there is a need for an improved battery pack that can be easily assembled and disassembled.